Lauren wants to know which location in her apartment is best for growing African violets. She has three African violets. She puts one on the balcony, one by the kitchen windows, and one on the mantel in the living room. Each plant has the same pot and the same soil, and Lauren gives each plant the same amount of water. Which is the independent variable?

First, before determining which variable is which, we go over the definition of each. The independent variable is the one which is intentionally changed in order to investigate its effect on the dependent variable. The dependent variable is monitored and changes occur in it due to the changing conditions of the independent variable. In this case, the location of the African violets is the independent variable as it is intentionally changed, while the rate of growth of the African violets is the dependent variable as it is being measured.  

it is either c or d and i know for sure it is not a or b

the answer is b.) hydrogen bonds between bases.